The invention relates to the general field of power apparatus for coupling and uncoupling threaded joints in articles of equipment or long pipe sections In assembling a string of tubing for an oil well a long series of pipe sections are screwed together usually by means of power tongs. In devices for screwing together pipes which after a termination of the boring operation are drawn into the bore hole for casing an earth bore it is known to use a unit consisting of a screw-in clamp and a counter device which can be used in either suspended execution, i.e. suspended on a cable or in a stationary execution.
Hydraulically biased jaws on power tong are known in the art, see for example U.S. Pat. Nos. 3,796,418, 3,921,473, 4,057,887, 4,402,293, and 4,712,284.
Although it is known in the art to use hydraulically powered jaws until now it has been necessary to alternately connect and disconnect the hydraulic power source from the power jaws to permit rotation of the jaws during the screwing and unscrewing actions (see U.S. Pat. No. 4,712,284 to Coyle, Sr. et al). The present invention provides an apparatus eliminating the need to couple and uncouple the hydraulic source from the jaws. In addition, the present invention provides for modifying the fluid pressure to obtain a multiplication of the available fluid pressure which is particularly useful for certain improved types of gripping apparatus such as that described in U.S. Pat. No. 4,989,909. The hydraulic power sources commonly available around many power tong applications do not provide high enough fluid pressures for certain improved gripping devices which are desirable because they are more protective of the expensive tubing used in some applications.
This invention therefore provides a novel fluid actuator for a hydraulically powered gripping device which combines a fluid pressure or force multiplication with the capability of a physical separation of the rotating jaws and the fluid power source to permit rotation of the jaws and any gripped object while maintaining clamping or gripping pressure.